Abstract
Men treated for localized prostate cancer by radiotherapy have often a remaining life span of 10 yr or more. Therefore, the risk for secondary malignancies should be taken into account. Plans for ten patients were evaluated which had been performed on an Oncentra® treatment planning system for a treatment with an Elekta Synergy™ linac with Agility™ head. The investigated techniques involved IMRT and VMTA with and without flattening filter. Different dose response models were applied for secondary carcinoma and sarcoma risk in the treated region and also in the periphery. As organs at risk we regarded for carcinoma risk urinary bladder, rectum, colon, esophagus, thyroid, and for sarcoma risk bone and soft tissue. The excess absolute risk (EAR) was found very similar in the treated region for both techniques (IMRT and VMAT) and also for both with and without flattening filter. The secondary sarcoma risk resulted about one magnitude smaller than the secondary carcinoma risk. The EAR to the peripheral organs was statistically significant reduced by application of the flattening filter free mode concerning the flattening filter as main source of scattered dose. Application of flattening filter free mode can thus support to reduce second malignancy risk for patients with localized prostate cancer.
Highlights
Prostate cancer is the most frequently diagnosed cancer among men in developed countries.[1]
The delineation of the regions of interest (ROI) in the therapy planning system (TPS) followed the description of Bos et al.[16]: The clinical target volume (CTV) was derived from the gross tumor volume (GTV) by adding a 5 mm three-dimensional margin excluding the rectal volume
Slight differences can be seen between intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) and between flattened beam (FB) and flattening filter free (FFF)
Summary
Prostate cancer is the most frequently diagnosed cancer among men in developed countries.[1]. Prostate cancer is a disease of elderly men, these patients have a remaining life span of 10 yr or more and the risk for secondary malignancies should be taken into account. Modern linear accelerators (linacs) promise shorter treatment times using the flattening filter free (FFF) mode. The flattening filter has been identified as the main source of scattered dose from the treatment head.[8,9] This dose might be responsible for additional secondary malignancy risk (SMR). Model calculations are regarded as a first essential step to evaluate this risk as long as clinical observations are not available.[10] Only a few investigations using model calculations have been published about the impact of the FFF mode on SMR. Besides works about patients with breast cancer,[11] ependymoma,[12] and pituitary adenoma[13] there is only one paper evaluating
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